Imaging of a patient's tissue has become a common screening and/or diagnostic tool in modern medicine. One example of such imaging is mammography, or the imaging of a patient's breast tissue. Breast cancer remains the most common cancer among women today, however, at this time there is no certain way to prevent breast cancer and the best strategy for dealing with breast cancer is early detection of the cancer so that it may be treated prior to metastatic spread. Accordingly, it is important for patients to have access to imaging techniques and systems that will detect very small cancers as early in their development as possible.
A three-dimensional imaging approach called “tomosynthesis” has been developed (see U.S. Pat. No. 5,872,828, which is incorporated herein by reference for its teachings relating to tomosynthesis systems and methods) which shows great promise for early detection of cancer. Tomosynthesis allows the reconstruction of a true volumetric distribution of absorption coefficients on the basis of the information contained in a series of projections acquired from a series of viewpoints about the target object. The viewpoint need not be regularly spaced, numerous, or arranged in any regular geometry. The tomosynthesis technique has been demonstrated to provide useful spatial differentiation of overlapping and nearby tissues at very high resolution comparable to projection 2D imaging, with approximately comparable radiation dose.
The problem of 3D reconstruction from tomosynthesis projections is difficult one. One promising technique for 3D reconstruction from tomosynthesis projections is provided in U.S. Provisional Patent Application Ser. No. 60/446,784, which is incorporated herein by reference. This technique applies a cone-beam geometry in an iterative forward-projection and back-projection method based on maximum-likelihood estimation of volumetric distribution of attenuation coefficients, using an estimation-maximization algorithm. However, the amount of computing power required to perform the 3D reconstruction will, for typical inexpensive computer systems, result in significant delays before the 3D reconstruction is available.